docs: def intersperse(lis, value):
      """Put value between each existing item in list.
  
      Parameters
      ----------
      lis : list
          List to intersperse.
      value : object
          Value to insert.
  
      Returns
      -------
      list
          interspersed list
      """
      out = [value] * (len(lis) * 2 - 1)
      out[0::2] = lis
      return out